Piezoelectric liquid inertia vibration eliminator

ABSTRACT

A tunable vibration isolator with active tuning elements having a housing, fluid chamber, and at least one tuning port. A piston is resiliently disposed within the housing. A vibration isolation fluid is disposed within the fluid chambers and the tuning ports. The tunable vibration isolator may employ either a solid tuning mass approach or a liquid tuning mass approach. The active vibration elements are preferably solid-state actuators.

BACKGROUND

1. Field of the Invention

The present invention relates in general to active vibration control.More specifically, the present invention relates to methods andapparatuses for isolating mechanical vibrations in structures or bodiesthat are subject to harmonic or oscillating displacements or forces. Thepresent invention is well suited for use in the field of aircraft, inparticular, helicopters and other rotary wing aircraft.

2. Description of Related Art

For many years, effort has been directed toward the design of apparatusfor isolating a vibrating body from transmitting its vibrations toanother body. Such apparatuses are useful in a variety of technicalfields in which it is desirable to isolate the vibration of anoscillating or vibrating device, such as an engine, from the remainderof the structure. Typical vibration isolation and attenuation devices(“isolators”) employ various combinations of the mechanical systemelements (springs and mass) to adjust the frequency responsecharacteristics of the overall system to achieve acceptable levels ofvibration in the structures of interest in the system. One field inwhich these isolators find a great deal of use is in aircraft, whereinvibration-isolation systems are utilized to isolate the fuselage orother portions of an aircraft from mechanical vibrations, such asharmonic vibrations, which are associated with the propulsion system,and which arise from the engine, transmission, and propellers or rotorsof the aircraft.

Vibration isolators are distinguishable from damping devices in theprior art that are erroneously referred to as “isolators.” A simpleforce equation for vibration is set forth as follows:

F=m{umlaut over (x)}+c{dot over (x)}+kz

A vibration isolator utilizes inertial forces (m{umlaut over (x)}) tocancel elastic forces (kx). On the other hand, a damping device isconcerned with utilizing dissipative effects (c{dot over (x)}) to removeenergy from a vibrating system.

One important engineering objective during the design of an aircraftvibration-isolation system is to minimize the length, weight, andoverall size including cross-section of the isolation device. This is aprimary objective of all engineering efforts relating to aircraft. It isespecially important in the design and manufacture of helicopters andother rotary wing aircraft, such as tilt rotor aircraft, which arerequired to hover against the dead weight of the craft, and which are,thus, somewhat constrained in their payload in comparison withfixed-wing aircraft.

Another important engineering objective during the design ofvibration-isolation systems is the conservation of the engineeringresources that have been expended in the design of other aspects of theaircraft or in the vibration-isolation system. In other words, it is animportant industry objective to make incremental improvements in theperformance of vibration isolation systems which do not require radicalre-engineering or complete redesign of all of the components which arepresent in the existing vibration-isolation systems.

A marked departure in the field of vibration isolation, particularly asapplied to aircraft and helicopters is disclosed in commonly assignedU.S. Pat. No. 4,236,607, titled “Vibration Suppression System,” issued 2Dec. 1980, to Halwes, et al. (Halwes '607). Halwes '607 is incorporatedherein by reference. Halwes '607 discloses a vibration isolator in whicha dense, low-viscosity fluid is used as the “tuning” mass tocounterbalance, or cancel, oscillating forces transmitted through theisolator. This isolator employs the principle that the acceleration ofan oscillating mass is 1800 out of phase with its displacement.

In Halwes '607, it was recognized that the inertial characteristics of adense, low-viscosity fluid, combined with a hydraulic advantageresulting from a piston arrangement, could harness the out-of-phaseacceleration to generate counter-balancing forces to attenuate or cancelvibration. Halwes '607 provided a much more compact, reliable, andefficient isolator than was provided in the prior art. The originaldense, low-viscosity fluid contemplated by Halwes '607 was mercury,which is toxic and highly corrosive.

Since Halwes' early invention, much of the effort in this area has beendirected toward replacing mercury as a fluid or to varying the dynamicresponse of a single isolator to attenuate differing vibration modes. Anexample of the latter is found in commonly assigned U.S. Pat. No.5,439,082, titled “Hydraulic Inertial Vibration Isolator,” issued 8 Aug.1995, to McKeown, et al. (McKeown '082). McKeown '082 is incorporatedherein by reference.

Several factors affect the performance and characteristics of theHalwes-type isolator, including the density and viscosity of the fluidemployed, the relative dimensions of components of the isolator, and thelike. One improvement in the design of such isolators is disclosed incommonly assigned U.S. Pat. No. 6,009,983, titled “Method and Apparatusfor Improved Isolation,” issued 4 Jan. 2000, to Stamps et al. (Stamps'983). In Stamps '983, a compound radius at the each end of the tuningpassage was employed to provide a marked improvement in the performanceof the isolator. Stamps '983 is incorporated herein by reference.

SUMMARY OF THE INVENTION

Although the foregoing inventions represent great strides in the area ofvibration isolation, certain shortcomings remain, in particular, theability to actively tune the isolator.

Therefore, it is an object of the present invention to provide avibration isolation system in which the isolator can be actively tuned.

It is another object of the present invention to provide a vibrationisolator that allows active tuning of the isolator, as well as,simultaneous vibration treatment of multiple harmonics.

It is yet another object of the present invention to provide a vibrationisolator that allows active tuning of the isolator, as well as, active“negative” damping which results in near zero vibrationtransmissibility.

It is yet another object of the present invention to provide a vibrationisolator that allows active tuning of the isolator by utilizingpiezoceramic elements for actuation.

These and other objectives are achieved by providing a tunable vibrationisolator with active tuning elements having a housing which definesfluid chambers. A piston is disposed within the housing. A vibrationisolation fluid is disposed within the fluid chambers. A passage havinga predetermined diameter extends through the piston to permit thevibration isolation fluid to flow from one fluid chamber to the other.The tunable vibration isolator may employ either a solid tuning massapproach or a liquid tuning mass approach. In either case, active tuningelements, or actuators, are disposed in the fluid chambers toselectively alter the dynamic characteristics of the vibration isolator.

Preferably, the relatively enlarged portion is defined by a compoundradius which extends over a predetermined length of the passage.

Additional objectives, features and advantages will be apparent in thewritten description which follows.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the application are setforth in the appended claims. However, the application itself, as wellas a preferred mode of use, and further objectives and advantagesthereof, will best be understood by reference to the following detaileddescription when read in conjunction with the accompanying drawings,wherein:

FIG. 1 is a perspective view of a helicopter according to the presentinvention;

FIG. 2A is a plan view of a tilt rotor aircraft according to the presentinvention in an airplane mode;

FIG. 2B is a perspective view of a tilt rotor aircraft according to thepresent invention in a helicopter mode;

FIG. 3 is a perspective view of a quad tilt rotor aircraft according tothe present invention in an airplane mode;

FIG. 4A is a cross-sectional view of a prior art liquid inertiavibration eliminator;

FIG. 4B is a force diagram of the prior art liquid inertia vibrationeliminator of FIG. 4A;

FIG. 4C is a plot of amplitude versus frequency for the prior art liquidinertia vibration eliminator of FIG. 4A;

FIG. 5A is a mechanical equivalent model of the preferred embodiment ofthe tunable vibration isolator according to the present invention;

FIG. 5B is a simplified schematic shown in cross section of the tunablevibration isolator of FIG. 5A;

FIG. 6A is a mechanical equivalent model of an alternate embodiment ofthe tunable vibration isolator according to the present invention;

FIG. 6B is a simplified schematic shown in cross section of the tunablevibration isolator of FIG. 6A;

FIG. 7A is a simplified schematic shown in cross section of anotheralternate embodiment of the tunable vibration isolator according to thepresent invention;

FIG. 7B is a simplified schematic shown in cross section of anotheralternate embodiment of the tunable vibration isolator according to thepresent invention;

FIG. 7C is a simplified schematic shown in cross section of anotheralternate embodiment of the tunable vibration isolator according to thepresent invention;

FIG. 7D is a simplified schematic shown in cross section of anotheralternate embodiment of the tunable vibration isolator according to thepresent invention;

FIG. 8 is a cross-sectional view of the preferred embodiment of thetunable vibration isolator according to the present invention;

FIG. 9 is a cross-sectional view of the an alternate embodiment of thetunable vibration isolator according to the present invention;

FIG. 10 is a cross-sectional view of a frequency step change mechanismfor use with the vibration isolator according to the present invention;

FIG. 11 is a perspective view of a fluid structure model of thevibration isolator according to the present invention;

FIG. 12 is a plot of vertical velocity versus fuselage station for thetunable vibration isolator according to the present invention;

FIG. 13 is a cross-sectional schematic showing the arrangement of thetwo sets of three active tuning elements according to the presentinvention taken at XIII-XIII of FIG. 8.

FIG. 14 is a cross-sectional view of an alternate embodiment of thetunable vibration isolator of FIG. 8;

FIG. 15 is an enlarged perspective view of the flow diverter of FIG. 14;

FIG. 16 is a cross-sectional schematic of another alternate embodimentof the tunable vibration isolator according to the present invention;

FIG. 17A is a cross-sectional view of another alternate embodiment ofthe tunable vibration isolator according to the present invention;

FIG. 17B is a chart demonstrating the active attenuation for the tunablevibration isolator of FIG. 17A;

FIG. 17C is a cross-sectional view of another alternate embodiment ofthe tunable vibration isolator according to the present invention;

FIG. 18 is a cross-sectional view of another alternate embodiment of thetunable vibration isolator according to the present invention;

FIGS. 19A-19C are the equations for the isolation frequency, the arearatios, and the length and number of turns of the fluid tuning passagefor the vibration isolator of FIG. 18;

FIGS. 20A and 20B are cross-sectional views of another alternateembodiment of the tunable vibration isolator according to the presentinvention;

FIG. 21 is a mechanical equivalent model for the alternate embodimentsof the tunable vibration isolators of FIGS. 17A, 17C, 18, 20A, and 20B;

FIG. 22A is a simplified schematic of an alternate embodiment of thetunable vibration isolator according to the present invention shown incross section;

FIG. 22B is a mechanical equivalent model of the tunable vibrationisolator of FIG. 22A;

FIG. 23A is a simplified schematic of an alternate embodiment of thetunable vibration isolator according to the present invention shown incross section;

FIG. 23B is a mechanical equivalent model of the tunable vibrationisolator of FIG. 23A;

FIG. 24 is a set of charts of the vibrations of the diesel engines of anaval vessel or ship according to the present invention;

FIG. 25A is a simplified schematic of the LIVE mount used on the navalvessel or ship;

FIG. 25B is a mechanical equivalent model for the LIVE mount of FIG.25A;

FIGS. 26A-26C are cross-sectional and perspective views of an exemplarymechanical design for the LIVE mount of FIG. 25A; and

FIG. 27 is a chart depicting the vibration attenuation of the LIVE mountof FIGS. 26A-26C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 in the drawings, a helicopter 11 according to thepresent invention is illustrated. Helicopter 11 has a fuselage 13 and amain rotor assembly 15, including main rotor blades 17 and a main rotorshaft 18. Helicopter 11 has a tail rotor assembly 19, including tailrotor blades 21 and a tail rotor shaft 20. Main rotor blades 17generally rotate about a vertical axis 16 of main rotor shaft 18. Tailrotor blades 21 generally rotate about a lateral axis 22 of tail rotorshaft 20. Helicopter 11 also includes a vibration isolation systemaccording to the present invention for isolating fuselage 13 or otherportions of helicopter 11 from mechanical vibrations, such as harmonicvibrations, which are associated with the propulsion system and whicharise from the engine, transmission, and rotors of helicopter 11.

The present invention may also be utilized on other types of rotary wingaircraft. Referring now to FIGS. 2A and 2B in the drawings, a tilt rotoraircraft 111 according to the present invention is illustrated. As isconventional with tilt rotor aircraft, rotor assemblies 113 a and 113 bare carried by wings 115 a and 115 b, and are disposed at end portions116 a and 116 b of wings 115 a and 115 b, respectively. Tilt rotorassemblies 113 a and 113 b include nacelles 120 a and 120 b, which carrythe engines and transmissions of tilt rotor aircraft 111, as well as,rotor hubs 119 a and 119 b on forward ends 121 a and 121 b of tilt rotorassemblies 113 a and 113 b, respectively.

Tilt rotor assemblies 113 a and 113 b move or rotate relative to wingmembers 115 a and 115 b between a helicopter mode in which tilt rotorassemblies 113 a and 113 b are tilted upward, such that tilt rotoraircraft 111 flies like a conventional helicopter; and an airplane modein which tilt rotor assemblies 113 a and 113 b are tilted forward, suchthat tilt rotor aircraft 111 flies like a conventional propeller drivenaircraft. In FIG. 2A, tilt rotor aircraft 111 is shown in the airplanemode; and in FIG. 2B, tilt rotor aircraft 111 is shown in the helicoptermode. As shown in FIGS. 2A and 2B, wings 115 a and 115 b are coupled toa fuselage 114. Tilt rotor aircraft 111 also includes a vibrationisolation system according to the present invention for isolatingfuselage 114 or other portions of tilt rotor aircraft 111 frommechanical vibrations, such as harmonic vibrations, which are associatedwith the propulsion system and which arise from the engines,transmissions, and rotors of tilt rotor aircraft 111.

Referring now to FIG. 3 in the drawings, a quad tilt rotor aircraft 211according to the present invention is illustrated. As with the tiltrotor aircraft of FIGS. 2A and 2B, rotor assemblies 213 a, 213 b, 213 c,and 213 d are carried by a forward wing 215 a, 215 c, and an aft wing215 b, 215 d, respectively. Tilt rotor assemblies 213 a, 213 b, 213 c,and 213 d include nacelles 220 a, 220 b, 220 c, and 220 d, which carrythe engines and transmissions of quad tilt rotor aircraft 211, as wellas, rotor hubs 219 a, 219 b, 219 c, and 219 d on forward ends of tiltrotor assemblies 213 a, 213 b, 213 c, and 213 d, respectively.

Tilt rotor assemblies 213 a, 213 b, 213 c, and 213 d move or rotaterelative to wing members 215 a, 215 b, 215 c, and 215 d between ahelicopter mode in which tilt rotor assemblies 213 a, 213 b, 213 c, and213 d are tilted upward, such that quad tilt rotor aircraft 211 flieslike a conventional helicopter; and an airplane mode in which tilt rotorassemblies 213 a, 213 b, 213 c, and 213 d are tilted forward, such thatquad tilt rotor aircraft 211 flies like a conventional propeller drivenaircraft. In FIG. 3, quad tilt rotor aircraft 111 is shown in theairplane mode. As shown in FIG. 3, wings 215 a, 215 b, 215 c, and 215 dare coupled to a fuselage 214. Tilt rotor aircraft 211 also includes avibration isolation system according to the present invention forisolating fuselage 214 or other portions of quad tilt rotor aircraft 211from mechanical vibrations, such as harmonic vibrations, which areassociated with the propulsion system and which arise from the engines,transmissions, and rotors of quad tilt rotor aircraft 211.

It should be understood that the present invention may be used with anyaircraft on which it would be desirable to have vibration isolationaccording to the present invention, including unmanned aerial vehiclesthat are remotely piloted.

Referring now to FIG. 4A in the drawings, a prior art liquid inertiavibration eliminator (LIVE unit) 327 for use on an aircraft isillustrated. Prior art LIVE unit 327 includes a housing 343 that has ahollow, generally cylindrical interior. A piston 347 of selectedcross-sectional diameter is disposed within the interior of housing 343.Housing 343 would typically be coupled to the fuselage of an aircraft(not shown) and piston 347 would typically be coupled to thetransmission and propulsion system of the aircraft (not shown) via apylon assembly at an attachment bracket 363. In such an arrangement, thefuselage serves as the body to be isolated from vibration, and thetransmission of the aircraft serves as the vibrating body. Anelastomeric seal and spring member 349 resiliently seals piston 347within the interior of housing 343.

A fluid chamber 361 is defined by the interior of housing 343 and piston347 and is sealed against leakage by elastomer member 349. Aknown-density, low-viscosity vibration-isolation fluid, also referred toas tuning fluid, is disposed within fluid chamber 361. In addition tosealing the vibration-isolation fluid in fluid chamber 361, elastomermember 349 functions as a spring to permit piston 347 to move oroscillate relative to housing 343, while maintaining piston 347 in acentral location in housing 343 when no load is applied.

A tuning port or passage 357 extends centrally through piston 347 andpermits the vibration-isolation fluid to move from one end of fluidchamber 361 to the other. A conical flow diverter 351 is provided ateach end of housing 343 and is aligned with and generally opposes theopening at each end of tuning passage 357. Each conical flow diverter351 enhances fluid flow by decelerating the vibration-isolation fluid asit flows from each end of the fluid chamber into and out of passage 357.

Referring now to FIG. 4B in the drawings, a mechanical equivalent model375 for the prior art LIVE unit 327 of FIG. 4A is illustrated. Inmechanical equivalent model 375, a box 377 represents the mass of thefuselage M_(fuselage); a box 379 represents the mass of the pylonassembly M_(pylon); and a box 381 represents the mass of the tuning massM_(t), in this case, the vibration-isolation fluid. A vibratory forceF·sin(ωt) is generated by the engine, transmission, and propulsionsystem. Force F·sin(ωt) is a function of the frequency of vibration ofthe transmission and propulsion system.

Force F·sin(ωt) causes an oscillatory displacement up of the pylonassembly; an oscillatory displacement of the fuselage u_(f); and anoscillatory displacement of the tuning mass u_(t). Elastomer member 349is represented by a spring 382 disposed between the fuselageM_(fuselage) and the pylon assembly M_(pylon). Spring 382 has a springconstant K.

In mechanical equivalent model 375, tuning mass M_(t) functions as ifcantilevered from a first fulcrum 383 attached to the pylon assemblyM_(pylon), and a second fulcrum 385 attached to the fuselageM_(fuselage). The distance a from first fulcrum 383 to second fulcrum385 represents the cross-sectional area of tuning port 357, and thedistance b from first fulcrum 383 to the tuning mass M_(t) representsthe effective cross-sectional area of piston 347, such that an arearatio, or hydraulic ratio, R is equal to the ratio of b to a. Mechanicalequivalent model 375 leads to the following equation of motion for thesystem:

${{\begin{bmatrix}{M_{pylon} + {\left( {R - 1} \right)^{2}M_{t}}} & {{- {R\left( {R - 1} \right)}}M_{t}} \\{{- {R\left( {R - 1} \right)}}M_{t}} & {M_{fuselage} + {R^{2}M_{t}}}\end{bmatrix}\begin{Bmatrix}{\overset{¨}{u}}_{p} \\{\overset{¨}{u}}_{f}\end{Bmatrix}} + {\begin{bmatrix}K & {- K} \\{- K} & K\end{bmatrix}\begin{Bmatrix}u_{p} \\u_{f}\end{Bmatrix}}} = \begin{Bmatrix}{{F\sin}\left( {\omega \; t} \right)} \\0\end{Bmatrix}$

As is evident, no means for actively tuning LIVE unit 327 is available.Once the cross-sectional areas of tuning passage 357 and piston 347 aredetermined, and the tuning fluid is chosen, the operation of LIVE unit327 is set, and cannot be altered without altering one or more of thesefeatures. On the other hand, the present invention provides a means ofactively tuning the functionality a LIVE unit during operation.

Referring now to FIG. 4C in the drawings, a plot of amplitude versusfrequency for LIVE unit 327 and mechanical equivalent model 375 isillustrated.

Referring now to FIG. 5A in the drawings, a mechanical equivalent model401 for the tunable vibration isolator according to the presentinvention is illustrated. The tunable vibration isolator of the presentinvention is preferably used to isolate the vibration generated by thetransmission and propulsion system of an aircraft, such as aircraft 11,111, and 211, from the fuselage, such as fuselages 14, 114, and 214 (seeFIGS. 1-3). However, it should be understood that although the tunablevibration isolator of the present invention is described herein withrespect to an aircraft application, it may be used in any application inwhich it is desirable to isolate the vibration between one body andanother. The following discussion of the preferred embodiment of thepresent invention will be with respect to an application of the tunablevibration isolator on quad tilt rotor aircraft 211 (see FIG. 3) toisolate the vibratory forces generated in forward wing 215 a, 215 c fromfuselage 214.

In mechanical equivalent model 401, fuselage 214 is represented as themass of the fuselage M_(fuselage), or box 403; forward wing 215 a, 215 cis represented as the mass of the wing M_(wing), or box 405; and a box407 represents the mass of the tuning mass M_(t), which in the presentinvention may be either a rod disposed in a tuning port or merelyvibration-isolation fluid disposed in the tuning port, as will bedescribed in detail below. In the preferred embodiment, the tuning massis a tungsten rod. A vibratory force F·sin(ωt) is generated by theengine, transmission, and propulsion system carried by nacelle 220 a atthe tip of wing 215 a. Force F·sin(ωt) is a function of the frequency ofvibration of the wing caused primarily by the transmission andpropulsion system.

Force F·sin(ωt) causes an oscillatory displacement u_(wing) of the wingM_(wing); an oscillatory displacement u_(fuselage) of the fuselageM_(fuselage); and an oscillatory displacement U_(tuning mass) of thetuning mass M_(t). As with the prior art LIVE unit 327, a spring member,represented by a spring 409, is disposed between the fuselageM_(fuselage) and the wing M_(wing). Spring 409 has a spring constant K.Spring 409 will be discussed in more detail below.

Tuning mass M_(t) is operably associated with fuselage M_(fuselage) andwing M_(wing). In mechanical equivalent model 401, tuning mass M_(t)functions as if cantilevered from a first fulcrum 411 attached to wingmember M_(wing), and a second fulcrum 413 attached to the fuselageM_(fuselage). The distance a from first fulcrum 411 to second fulcrum413 represents the cross-sectional area of the tuning rod or port, andthe distance b from first fulcrum 411 to the tuning mass M_(t)represents the effective cross-sectional area of a piston (see 455 inFIG. 5B), such that an area ratio, or hydraulic ratio, R is equal to theratio of b to a.

An active tuning element 415 is disposed between the wing memberM_(wing) and the tuning mass M_(t). Active tuning element 415 functionsto make fulcrum 411 vibrate. It should be understood that active tuningelement 415 may represent a plurality of active tuning elements actingeither together or independently. In the preferred embodiment, threepairs of active tuning elements are employed, as will be discussed inmore detail below. In the preferred embodiment, active tuning element415 is a piezoceramic element that oscillates in the range of about 16.6Hz to 19.9 Hz to counteract the vibration of the wing member M_(wing).It should be understood that active tuning element 415 may be comprisedof other smart materials, such as electrostrictive materials,magnetostrictive materials, or may comprise other means, such aselectromagnetic, pneumatic, hydraulic, or other possible means.

Active tuning element 415 can be represented by mechanical propertiesinclude a spring element 417 having a spring constant k_(p), a massM_(p), and a controllable force element 421. Controllable force element421 may have any phase angle and be of any magnitude within the maximumcapabilities of active tuning element 415. Active tuning element 415also includes control circuitry (not shown) for controlling theactuation of active tuning element 415. Active tuning element 415 allowsfor selective actuation of the tuning mass. Mechanical equivalent model401 leads to the following equation of motion for the system:

${{\begin{bmatrix}{M_{fuselage} + {\left( {R - 1} \right)^{2}M_{t}}} & {{- {R\left( {R - 1} \right)}}M_{t}} & 0 \\{{- {R\left( {R - 1} \right)}}M_{t}} & {M_{wing} + {R^{2}M_{t}}} & 0 \\0 & 0 & M_{p}\end{bmatrix}\begin{Bmatrix}{\overset{¨}{u}}_{fuselage} \\{\overset{¨}{u}}_{wing} \\{\overset{¨}{u}}_{actuator}\end{Bmatrix}} + {\begin{bmatrix}K & {- K} & 0 \\{- K} & {K + k_{p}} & {- k_{p}} \\0 & {- k_{p}} & k_{p}\end{bmatrix}\begin{Bmatrix}u_{fuselage} \\u_{wing} \\u_{actuator}\end{Bmatrix}}} = \begin{Bmatrix}F_{p} \\0 \\{- F_{p}}\end{Bmatrix}$

Referring now to FIG. 5B in the drawings, a simplified schematic of thepreferred embodiment of a vibration isolator 451 according to thepresent invention is illustrated. Vibration isolator 451 includes ahousing 453 having a hollow, generally cylindrical interior. Housing 453would typically be coupled to the fuselage of the aircraft, i.e., thebody being isolated from the vibration. A piston 455 of selectedcross-sectional diameter is disposed within the interior of housing 453.Piston 455 would typically be coupled to the wing of the aircraft, i.e.,the source of the vibration. A first elastomeric seal and spring member457 resiliently seals piston 455 within the interior of housing 453.

A fluid chamber 459 is defined by the interior of housing 453 and piston455. A known-density, vibration-isolation fluid 461, also referred to astuning fluid, is disposed within fluid chamber 459. Tuning fluid 461 ispreferably non-corrosive and environmentally safe, being low-viscosityand having a relatively high density. In addition to sealing tuningfluid 461 within fluid chamber 459, first elastomeric member 457functions as a spring to permit piston 455 to move or oscillate relativeto housing 453, while maintaining piston 455 in a central locationwithin housing 453 when no load is applied. A tuning port 463 extendscentrally through piston 455 and permits tuning fluid 461 to move fromone end of fluid chamber 459 to the other.

A first actuating piston 465 is disposed within fluid chamber 461 at oneend of vibration isolator 451. A second actuating piston 467 is disposedwithin fluid chamber 461 at the opposing end of vibration isolator 451.A second elastomeric seal and spring member 469 resiliently seals firstactuating piston 465 within the interior of housing 453. In a similarfashion, a third elastomeric seal and spring member 471 resilientlyseals second actuating piston 467 within the interior of housing 453. Afirst tunable active tuning element 473, operably associated with firstactuating piston 465, is coupled to housing 453. In a similar fashion, asecond tunable active tuning element 475, operably associated withsecond actuating piston 467, is also coupled to housing 453. First andsecond active tuning elements 473, 475 are each electrically coupled tocontrol circuitry (not shown) for controlling the actuation of first andsecond actuating pistons 465, 467, respectively.

In this simplified representation, the engine, transmission, andpropulsion system produce oscillatory forces which are transmittedthrough the wing member causing an oscillatory displacement u_(wing) ofpiston 455. The displacement u_(wing) of piston 455 is transmittedthrough elastomeric member 457 to the fuselage of the aircraft viahousing 453 resulting in a displacement u_(fuselage). Tuning fluid 461within tuning port 463 opposes the oscillatory displacement u_(wing) ofthe piston 455 with a displacement u_(tuning) mass of tuning fluid 461.In addition, first and second active tuning elements 473, 475 arecontrolled by the control circuitry to selectively actuate first andsecond actuation pistons 465, 467 resulting in displacementsu_(actuator) of first and second actuating pistons 465, 467. Actuationof first and second actuating pistons 465, 467 at a selected frequencyand amplitude amplifies the displacement u_(tuning mass) of tuning fluid461 and cancels out the frequency of the oscillatory forces from thewing member. In this manner the oscillatory vibration from the engine,transmission, and propulsion are not transferred through the wing memberto the fuselage.

It should be understood that the location of active tuning element 415does not affect its functionality. This concept is illustrated withrespect to FIGS. 6A and 6B. In FIG. 6A, mechanical equivalent model 401is again illustrated. The only difference in mechanical equivalent model401 between FIG. 5A and FIG. 6A is the location of active tuning element415. In FIG. 5A, active tuning element 415 is disposed between the wingmember M_(wing) and the tuning mass M_(t); however, in FIG. 6A, activetuning element 415 is disposed between the fuselage M_(fuselage) and thetuning mass M_(t). In other words, active tuning element 415 may act oneither the vibrating body or the body to be isolated from vibration. Theequation of motion for the system of FIG. 6A is similar to the equationof motion for the system of FIG. 5A.

Referring now to FIG. 6B in the drawings, a simplified schematic of analternate embodiment of a vibration isolator 551 according to thepresent invention is illustrated. Vibration isolator 551 includes ahousing 553 having a hollow, generally cylindrical interior. Housing 553would typically be coupled to the fuselage of the aircraft, i.e., thebody being isolated from the vibration. A piston 555 of selectedcross-sectional diameter is disposed within the interior of housing 553.Piston 555 would typically be coupled to the wing of the aircraft, i.e.,the source of the vibration, via a mounting bracket 556 extends outsideof and around housing 553. A first elastomeric seal and spring member557 resiliently seals piston 555 within the interior of housing 553.

A fluid chamber 559 is defined by the interior of housing 553 and piston555. A known-density, vibration-isolation fluid 561, similar in form andfunction to tuning fluid 461, is disposed within fluid chamber 559.Tuning fluid 561 is preferably non-corrosive and environmentally safe,being low-viscosity and having a relatively high density. In addition tosealing tuning fluid 561 within fluid chamber 559, first elastomericmember 557 functions as a spring to permit piston 555 to move oroscillate relative to housing 553, while maintaining piston 555 in acentral location within housing 553 when no load is applied. A tuningport 563 extends centrally through piston 555 and permits tuning fluid561 to move from one end of fluid chamber 559 to the other.

An actuation assembly 560 is coupled to the wing of the aircraft at amounting point 562. A first tunable active tuning element 573 isdisposed within actuation assembly 560, such that first active tuningelement 573 may act upon mounting bracket 556 in one direction,preferably coaxial with tuning port 563. In a similar fashion, a secondtunable active tuning element 575 is disposed within actuation assembly560, such that second active tuning element may act upon mountingbracket 556 in an opposing direction to that of first active tuningelement 577. Apertures 569 and 571 through actuation assembly 560 allowmovement of mounting bracket 556 relative to actuation assembly 560.Actuation assembly 560 is coupled to mounting bracket 556 via a spring542. Because first and second active tuning elements 573, 575 act uponmounting bracket 556, the actuation of first and second active tuningelements 573, 575 are transferred through mounting bracket 556 to piston555. First and second active tuning elements 573, 575 are eachelectrically coupled to control circuitry (not shown) for controllingthe actuation of mounting bracket 556.

In this simplified representation, the engine, transmission, andpropulsion system produce oscillatory forces which are transmittedthrough the wing member causing an oscillatory displacement u_(wing) ofpiston 555. The displacement u_(wing) of piston 555 is transmittedthrough elastomeric member 557 to the fuselage of the aircraft viahousing 553 resulting in a displacement u_(fuselage). Tuning fluid 561within tuning port 563 opposes the oscillatory displacement u_(wing) ofthe piston 555 with a displacement u_(tuning) mass of tuning fluid 561.In addition, first and second active tuning elements 573, 575 arecontrolled by the control circuitry to selectively actuate mountingbracket 556 resulting in a displacement u_(actuator) of actuationassembly 560. Actuation of actuation assembly at a selected frequencyand amplitude amplifies the displacement u_(tuning mass) of tuning fluid561 and cancels out the frequency of the oscillatory forces from thewing member. In this manner the oscillatory vibration from the engine,transmission, and propulsion are not transferred through the wing memberto the fuselage.

Referring now to FIGS. 7A-7D in the drawings, simplified schematics ofadditional alternate embodiments of the vibration isolator according tothe present invention are illustrated. In FIG. 7A, a simplifiedschematic of a vibration isolator 651 according to the present inventionis illustrated. Vibration isolator 651 includes a housing 653 having ahollow, generally cylindrical interior. Housing 653 would typically becoupled to the fuselage of the aircraft, i.e., the body being isolatedfrom the vibration. A piston 655 of selected cross-sectional diameter isdisposed within the interior of housing 653. Piston 655 would typicallybe coupled to the wing of the aircraft, i.e., the source of thevibration, via a pylon mounting bracket 656. A first elastomeric sealand spring member 657 resiliently seals piston 655 within the interiorof housing 653.

A fluid chamber 659 is defined by the interior of housing 653 and piston655. A known-density, vibration-isolation tuning fluid 661 is disposedwithin fluid chamber 659. In addition to sealing tuning fluid 661 withinfluid chamber 659, first elastomeric member 657 functions as a spring topermit piston 655 to move or oscillate relative to housing 653, whilemaintaining piston 655 in a central location within housing 653 when noload is applied. A tuning port 663 extends centrally through piston 655and permits tuning fluid 661 to move from one end of fluid chamber 659to the other. A tuning mass, or tuning rod 660, is disposed withintuning port 663. Tuning rod 660 oscillates within tuning port inresponse to oscillatory movement of piston 655 and tuning fluid 661. Aplurality of optional bypass ports (not shown) through piston 655restrict the axial motion of tuning rod 660.

A first tunable active tuning element 673 is disposed within housing 653at one end of fluid chamber 659. In a similar fashion, a second activetuning element 675 is disposed within housing 653 at an opposing end offluid chamber 659. A hydraulic ratio R is equal to the ratio of the areaA_(o) of first and second active tuning elements 673, 675 to the areaA_(j) of tuning port 663.

In FIG. 7B, a simplified schematic for another vibration isolator 681according to the present invention is illustrated. Vibration isolator681 includes a housing 683 having a hollow, generally cylindricalinterior. Housing 683 would typically be coupled to the fuselage of theaircraft, i.e., the body being isolated from the vibration. A piston 685of selected cross-sectional diameter A_(j) is disposed within theinterior of housing 683. In this embodiment, piston 685 would typicallybe coupled to the floor of the aircraft, i.e., the source of thevibration. An elastomeric seal and spring member 688 resiliently sealspiston 685 within the interior of housing 683.

A fluid chamber 687 is defined by the interior of housing 683 and piston685. A known-density, vibration-isolation tuning fluid 689 is disposedwithin fluid chamber 687. In addition to sealing tuning fluid 689 withinfluid chamber 687, elastomeric member 688 functions as a spring topermit piston 685 to move or oscillate relative to housing 683, whilemaintaining piston 685 in a central location within housing 683 when noload is applied.

A tunable active tuning element 689 is disposed within housing 683 atone end of fluid chamber 687. Active tuning element 689 has across-sectional area A_(o). A hydraulic ratio R is equal to the ratio ofthe cross-sectional area A_(o) of active tuning element 689 to thecross-sectional area A_(j) of piston 685. In this embodiment, there isno tuning port or tuning mass, and active tuning element 689 acts uponpiston 685 via fluid 689 to counteract oscillatory forces transferred topiston 685 by the floor of the aircraft.

In FIG. 7C, a simplified schematic for another vibration isolator 691according to the present invention is illustrated. Vibration isolator691 is configured from two vibration isolators 681 placed end to end.Vibration isolator 691 comprises a housing 693 having a hollow,generally cylindrical interior. Housing 693 would typically be coupledto the fuselage of the aircraft, i.e., the body being isolated from thevibration. A piston 695 of selected cross-sectional diameter A_(j) isdisposed within the interior of housing 693. In this embodiment, piston695 would typically be coupled to the floor of the aircraft, i.e., thesource of the vibration. An elastomeric seal and spring member 697resiliently seals piston 695 within the interior of housing 683.

A first fluid chamber 699 is defined by the interior of housing 693 andpiston 695. Likewise, a second fluid chamber 701 is defined by theinterior of housing 693 and piston 695. An incompressible fluid 703 isdisposed within fluid chambers 699 and 701. In addition to sealing fluid703 within fluid chambers 699, 701, elastomeric member 697 functions asa spring to permit piston 695 to move or oscillate relative to housing693, while maintaining piston 695 in a central location within housing693 when no load is applied.

A first tunable active tuning element 705 is disposed within housing 693at one end of fluid chamber 699. In a similar fashion, a second tunableactive tuning element 707 is disposed within housing 693 at the opposingend of fluid chamber 701. Active tuning elements 705, 707 have across-sectional area A_(o). A hydraulic ratio R is equal to the ratio ofthe cross-sectional area A_(o) of active tuning elements 705, 707 to thecross-sectional area A_(j) of piston 695. In this embodiment, there isno tuning port and, thus, no tuning mass; and active tuning elements705, 707 act upon piston 695 via fluid 703 to counteract oscillatoryforces transferred to piston 695 by the floor of the aircraft. Anoptional small passage 709 may pass through piston 695 so as to placefluid chamber 699 into fluid communication with fluid chamber 701.Passage 709 allows for very low frequency mean shifts of piston 695.

In FIG. 7D, a simplified schematic for another vibration isolator 721according to the present invention is illustrated. Vibration isolator721 is similar to vibration isolator 451 of FIG. 5B with the exceptionthat the piston assembly is configured differently. Vibration isolator721 includes a housing 723 having a hollow, generally cylindricalinterior. Housing 723 would typically be coupled to the fuselage of theaircraft, i.e., the body being isolated from the vibration. A piston 725of selected cross-sectional diameter is disposed within the interior ofhousing 723. Piston 725 would typically be coupled to the wing or engineof the aircraft, i.e., the source of the vibration. A first elastomericseal and spring member 727 resiliently seals piston 725 within theinterior of housing 723.

A fluid chamber 729 is defined by the interior of housing 723 and piston725. A known-density, vibration-isolation fluid 731, also referred to astuning fluid, is disposed within fluid chamber 729. Tuning fluid 731 ispreferably non-corrosive and environmentally safe, being low-viscosityand having a relatively high density. Fluid chamber 729 includes centralfluid channels 733 a and 733 b on either side of piston 725.

In addition to sealing tuning fluid 731 within fluid chamber 729, firstelastomeric member 727 functions as a spring to permit piston 725 tomove or oscillate relative to housing 723, while maintaining piston 725in a central location within housing 723 when no load is applied. Atuning port 735 extends centrally through piston 725 and permits tuningfluid 731 to move from one end of fluid chamber 729 to the other. Insuch an embodiment, tuning port 735 might have a diameter of about 0.03inches.

A first actuating piston 737 is disposed within fluid chamber 729 at oneend of vibration isolator 721. A second actuating piston 739 is disposedwithin fluid chamber 729 at the opposing end of vibration isolator 721.A second elastomeric seal and spring member 741 resiliently seals firstactuating piston 737 within the interior of housing 723. In a similarfashion, a third elastomeric seal and spring member 743 resilientlyseals second actuating piston 739 within the interior of housing 723. Afirst tunable active tuning element 745, operably associated with firstactuating piston 737, is coupled to housing 723. In a similar fashion, asecond tunable active tuning element 747, operably associated withsecond actuating piston 739, is also coupled to housing 723. First andsecond active tuning elements 745, 747 are each electrically coupled tocontrol circuitry (not shown) for controlling the actuation of first andsecond actuating pistons 737 and 739, respectively.

In this simplified representation, the engine, transmission, andpropulsion system produce oscillatory forces which are transmittedthrough the wing member causing an oscillatory displacement u_(wing) ofpiston 725. The displacement u_(wing) of piston 725 is transmittedthrough elastomeric member 727 to the fuselage of the aircraft viahousing 723 resulting in a displacement u_(fuselage). Tuning fluid 731within tuning channels 733 a and 733 b, and within tuning port 735opposes the oscillatory displacement u_(wing) of the piston 725 with adisplacement u_(tuning mass) of tuning fluid 731. In addition, first andsecond active tuning elements 745, 747 are controlled by the controlcircuitry to selectively actuate first and second actuation pistons 737,739 resulting in displacements u_(actuator) of first and secondactuating pistons 737, 739. Actuation of first and second actuatingpistons 737, 739 at a selected frequency and amplitude amplifies thedisplacement u_(tuning mass) of tuning fluid 731 and cancels out thefrequency of the oscillatory forces from the wing member. In this mannerthe oscillatory vibration from the engine, transmission, and propulsionare not transferred through the wing member to the fuselage.

In particular, the embodiments of FIGS. 7C and 7D provide a uniquecapability of eliminating high steady pressure from active tuningelements 705, 707, 745, and 747 by segregating the large steady meanpressure from the oscillatory pressure. This allows active tuningelements 705, 707, 745, and 747 to operate more efficiently by stayingwithin the allowed pressures for the materials used to form activetuning elements 705, 707, 745, and 747. Without such means, high steadypressures could be introduced due to ground-air-ground cycles in whichthe pylon or wing member starts at rest compressing the vibrationisolator. As lift is increased, the load is lifted to a zero compressiveload, and then further, such that the fuselage is suspended from thevibration isolator, placing the vibration isolator in tension. Thisresults in very large mean pressures. For example, if active tuningelement 705, 707, 745, or 747 is a piezoceramic material, it would havea maximum operating pressure of about 2,000 to 4,000 pounds per squareinch. By eliminating the large mean pressure shift, the active tuningelements 705, 707, 745, and 747 can operate more efficiently withoutfailing.

Referring now to FIGS. 8 and 13 in the drawings, the preferredembodiment of a physical configuration of a LIVE unit 801 according tothe present invention is illustrated in a cross-sectional view. AlthoughLIVE unit 801 will be described herein with reference to “uppercomponents and “lower” components, it will be understood that LIVE unit801 functions independent of its orientation. LIVE unit 801 is installedon aircraft 11, 111, or 211. LIVE unit 801 includes a housing 803 havinga hollow, generally cylindrical interior having a longitudinal axis 802.Housing 803 is coupled to the fuselage of the aircraft, i.e., the bodybeing isolated from the vibration, at mounting apertures 804. A piston805 of selected cross-sectional diameter is disposed within the interiorof housing 803. Piston 805 is coupled to the wing members of theaircraft, i.e., the source of the vibration, as will be explained below.Piston 805 includes an upper convex flange 807 and an opposing lowerconvex flange 808.

Upper convex flange 807 is coupled to an upper elastomeric seal member809, and lower convex flange 808 is coupled to a lower elastomeric sealmember 810. Upper and lower elastomeric seal members 809 and 810 includeinner steel rings 809 a and 810 a for coupling to upper and lower convexflanges 807 and 808 of piston 805, central elastomeric seals 809 b and810 b to seal a tuning fluid 812 within LIVE unit 801, and outer steelrings 809 c and 810 c for coupling to an upper spacer 814 and a lowerspacer 816, respectively. Preferably, upper and lower elastomeric sealmembers 809 and 810 each have an effective diameter of about 6.00inches.

An upper fluid chamber 831 is generally defined by upper convex flange807, upper elastomeric seal member 809, and an upper cap 833. Upper cap833 includes a mounting aperture 835 for coupling LIVE unit 801 to thewing member of the aircraft. In a similar fashion, a lower fluid chamber837 is generally defined by lower convex flange 808, lower elastomericseal member 810, and a lower cap 839. A vibration isolation fluid, ortuning fluid, 841 fills upper and lower fluid chambers 831 and 837.Tuning fluid 841 is preferably a silicone oil with low viscosity. Such atuning fluid 841 provides good lubricity with low density. Having avirtually incompressible liquid with reasonably low density reduces theparasitic weight in upper and lower fluid chambers 831 and 837.

An upper concave plate 811 is matingly in force transference contactwith upper convex flange 807. In a similar fashion, an opposing lowerconcave plate 813 is matingly in force transference contact with lowerconvex flange 808. Upper and lower concave plates 811 and 813 areconfigured to receive a plurality of piston receiver plates 815. In asimilar fashion, housing 803 is configured to receive a plurality ofhousing receiver plates 817. Piston receiver plates 815 and housingreceiver plates 817 are paired together, such that each pair receivesone of a plurality of active tuning elements 819 a and 819 b. Activetuning elements are electrically coupled to and controlled by controlcircuitry (not shown) via electrical leads 820 which pass throughapertures 824 in housing 803. In the preferred embodiment, active tuningelements 819 a and 819 b are piezoceramic elements that oscillate in therange of about 16.6 Hz (airplane mode operation) to about 19.9 Hz(helicopter mode operation) to counteract the vibration of the wingmember. It should be understood that active tuning elements 819 a and819 b may be comprised of other smart materials, such aselectrostrictive, magnetostrictive, or may comprise other means, such aselectromagnetic, pneumatic, hydraulic, or other possible means.

It is desirable that active tuning elements 819 a and 819 b act in alongitudinal direction only. Therefore, in the preferred embodiment ofthe present invention, six active tuning elements are spatially alignedaround LIVE unit 801, such that three extend downward from the upperportion of housing 803, i.e., 819 b; and three extend upward from thelower portion of housing 803, i.e., 819 a. Because three points define aplane, the mating of upper and lower concave plates 811 and 813 to upperand lower convex flanges 807 and 808 of piston 805 serves to equalizethe load between the three pairs of active tuning elements 819 a and 819b. Loads in active tuning elements 819 a and 819 b remain essentiallyaxial along axis 802, thereby minimizing moments. To further reduceundesirable moments, each active tuning element 819 a and 819 b includesa hemispherical end cap 821 on each end; and a thin elastomeric layerinterface 823 is disposed between each end cap 821 and each pistonreceiver plate 815 and each housing receiver plate 817. In addition, anupper anti-rotation flexure 845 is disposed between and coupled tohousing 803 and upper concave plate 811. Likewise, a lower anti-rotationflexure 847 is disposed between and coupled to housing 803 and lowerconcave plate 813. Anti-rotation flexures 845 and 847 are preferablysteel strips which ensure that upper and lower concave plates 811 and813 may move in the axial direction relative to housing 803, but may notrotate relative to housing 803.

The spring force between housing 803 and piston 805 is provided by anupper spring plate assembly 861 and a lower spring plate assembly 863.Upper and lower spring plate assemblies 861 and 863 provide a stiffnessof about 300,000 pounds per inch. Upper and lower spring plateassemblies 861 and 863 are configured to allow piston 805 to oscillatein the axial direction relative to housing 803.

The components of LIVE unit 801 are resiliently held together by aplurality of fasteners 851 which align and clamp together lower cap 839,lower spacer 816, lower spring plate assembly 863, housing 803, upperspring plate assembly 861, upper spacer 814, and upper cap 833.

A central channel 871 extends axially through the center of piston 805.In the preferred embodiment, central channel 871 receives a tubularshaft 873. Tubular shaft 873 is retained within tuning central channel871 by clamping a flange portion 879 between retaining rings 875 and877. A pin 880 may be used to secure retaining ring 877 in place.

Tubular shaft 873 includes an axial tuning port 881, preferably having adiameter of about 0.687 inches. A tuning mass 883 is a rigid bodyslidingly disposed within tuning port 881. Tuning mass 883 is preferablya tungsten rod. Tuning mass 883 may be one of at least two differentweights: (1) a heavier one for airplane mode operation at 16.6 Hz; and(2) a lighter one for helicopter mode operation at 19.9 Hz. An upperbumper 860 and a lower bumper 862 protect tuning mass 883, upper cap833, and lower cap 839 from damage in the event of an over-travel bytuning mass 883.

An upper guide ring 885 and a lower guide ring 887, each preferably madeof brass, align and guide tuning mass 883 as tuning mass 883 slides upand down in tuning port 881 in response to oscillatory forces from thewing member of the aircraft. In addition, upper and lower guide rings885 and 887 allow activation of an upper one-way bypass port 889 and alower one-way bypass port 891, depending upon the axial location oftuning mass 883. Upper and lower bypass ports 889 and 891 preventovertravel of the tuning mass during large changes in steady orquasisteady loads, such as would occur during ground-air-ground cyclesor maneuvers. Upper and lower bypass ports 889 and 891 provide fluidcommunication between upper and lower fluid chambers 831 and 837, andallow the liquid pressures in upper and lower fluid chambers 831 and 837to equalize when the amplitude of the oscillatory motion of tuning mass883 is sufficiently large, thereby limiting the amplitude of tuning mass883. Thus when guide rings 885 and 887 travel beyond the closest bypassport 889 or 891, the pressures in upper and lower fluid chambers 831 and837 equalize and the velocity of tuning mass 883 peaks.

One-way flapper valves (not shown) are located in the bypass passage andcover the backside of bypass ports 889 and 891. The bypass passages andassociated one-way flapper valves act to center the oscillating tuningmass 883 axially within tuning port 881.

Referring now to FIG. 9 in the drawings, an alternate embodiment of aphysical configuration of a vibration isolator 901 according to thepresent invention is illustrated in a cross-sectional view. All of thecomponents of vibration isolator 901 are identical in form and functionas the components of LIVE unit 801, with the exception that tubularshaft 873 and tuning mass 883 has been replaced with a tubular flow port903. Tubular flow port 903 includes a central tuning passage 904.Tubular flow port 903 is configured to seal off upper and lower bypassvalves 889 and 891. No solid tuning mass is necessary in vibrationisolator 901. In other words, LIVE unit 801 uses a solid tuning massapproach, and vibration isolator 903 uses a liquid tuning mass approach.

It is preferred that the diameter of central tuning passage 904 makesthe area ratio, or hydraulic ratio, R, for liquid tuning mass equal to360. This amplification ratio may result in high viscous damping due tothe high fluid velocity. However, this approach offers a reducedcomplexity design.

In the liquid tuning mass approach of FIG. 9, tuning fluid 906 ispreferably non-corrosive and environmentally safe, being low-viscosityand having a relatively high density. The silicone oil which ispreferred in the solid tuning mass approach of FIG. 8 is not used in theliquid tuning mass approach, because it is desirable that the liquidtuning mass have greater density with slightly less viscosity. Althoughthe tuning mass liquid's lubricity properties are not as good assilicone oil, there is no need for good lubricity because there are nosliding parts in the liquid tuning mass approach.

Referring now to FIG. 10 in the drawings, a frequency step changemechanism 951 is illustrated. Frequency step change mechanism 951 allowsstep tuning for treating principal vibration at two differentfrequencies, such as 16.6 Hz and 19.9 Hz. Frequency step changemechanism 951 may be used in place of upper and lower elastomeric sealmembers 809 and 810. Frequency step change mechanism 951 includes anouter housing 953, an inner housing 955, and an intermediate ring 957.An inner-upper elastomer 959 and an inner-lower elastomer 961 aredisposed between inner housing 955 and intermediate ring 957. Anouter-upper elastomer 963 and an outer-lower elastomer 965 are disposedbetween inner housing 955 and intermediate ring 957. A shuttle pin 966locks intermediate ring 957 to either inner housing 955 or outer housing953. When locked to inner housing 955, the effective piston radius isr₁. When locked to outer housing 953, the effective piston radius is r₂.For example, with the liquid tuning approach of FIG. 9, the outer pistonradius, r₁, results in an area ratio R=360.5, providing a passive(open-loop) isolation frequency of 16.6 Hz. To increase the isolationfrequency to 19.9 Hz, the area ratio, R, must be decreased toapproximately 300. This can be accomplished by sliding shuttle pin 966radially inward, thereby locking out outer-upper and outer-lowerelastomers 963 and 965, and releasing inner-upper and inner-lowerelastomers 959 and 961, so that the piston radius becomes r₂. With aseparation between the inner and outer elastomers, the piston radius isreduced, decreasing the area ratio, R, to 300.8.

Referring now to FIG. 11 in the drawings, a coupled fluid structuremodel of the vibration isolator 973 of the present invention isillustrated. A computer generated analytical model of vibration isolator973 was created and analyzed to determine the driving point stiffness atthe active tuning element input. The static stiffness of vibrationisolator 973 was analyzed by fixing a tuning mass 970 to a piston 972.An actuation force was applied across stack actuators 974, and thedriving point displacement was calculated. From this analysis, thedriving point stiffness was determined to be about the same total axialstiffness of the six piezoceramic actuators alone. Thus, the efficiencymay be reduced because some of the actuator motion may be used toelastically strain the structure of vibration isolator 973, rather thanproviding useful work in accelerating tuning mass 972.

Referring now to FIG. 12 in the drawings, a computer generated plot 975of vertical velocity versus fuselage station for the tunable vibrationisolator according to the present invention, as used on quad tilt rotoraircraft 211 of FIG. 3, is illustrated. Plot 975 shows the fuselagevibration envelope for the vibration isolator of the present invention.Region 977 is a high baseline region representing no vibrationisolation; region 979 is a passive region representing vibrationisolation without active tuning having; and region 981 represents anactive region with active tuning of vibration isolation.

Referring now to FIGS. 14 and 15 in the drawings, a LIVE unit 991, whichis an alternate embodiment of LIVE unit 801, is illustrated. In thisembodiment, upper bumper 860 and lower bumper 862 of LIVE unit 801 arereplaced by flow diverters 993 and 995. Flow diverters 993 and 995 aregenerally conical in shape, preferably having a slightly concavedsurface. As is shown in FIG. 15, flow diverters 993 and 995 may includeinstallation apertures 997 to facilitate the installation of flowdiverters 993 and 995 into upper cap 833 and lower cap 839. It will beappreciated that other suitable installation means may be utilized. Itis preferred that installation apertures be plugged after installationto provide a smooth surface for diverting the tuning fluid. Flowdiverters 993 and 995 divert the flow of the tuning fluid andsignificantly increase the performance of LIVE unit 991.

Referring now to FIG. 16 in the drawings, an alternate embodiment of thevibration isolator of the present invention is illustrated. In thisembodiment, a dual frequency LIVE unit 1051, similar to LIVE unit 801,includes a means for actively tuning the frequency of the unit. LIVEunit 1051 includes a main housing 1053 having a mounting portion 1054that is configured for attachment to a structure for which vibration isto be isolated, such as the fuselage of an aircraft.

A piston 1063 is resiliently coupled to main housing 1053 by elastomericseals 1065. Piston 1063, main housing 1053, and elastomeric seals 1065define an upper fluid chamber 1067 and a lower fluid chamber 1069. Afluid tuning passage 1071 passes axially through piston 1063, so as toplace upper fluid chamber 1067 and lower fluid chamber 1069 in fluidcommunication. Flow diverters 1066 and 1068, similar to flow diverters993 and 995, are disposed within upper fluid chamber 1067 and lowerfluid chamber 1069, respectively. The axial length of tuning passage1071 may be selectively changed by adjusting a trombone-type slidingtuner 1073.

Tuner 1073 includes a fluid exit port 1075 on one end and an elongatedtubular shaft 1077 that telescopes into fluid tuning passage 1071 on theother end. Tuner 1073 operates between an extended position, which isshown in FIG. 16, and a retracted position, in which exit port 1075 isretracted downward against the upper surface of piston 1063. When tuner1073 is in the extended position, LIVE unit 1051 operates at a firstselected frequency; and when tuner 1073 is in the retracted position,LIVE unit 1051 operates at a higher, second selected frequency. In thepreferred embodiment, the first frequency is about 16.6 Hz, and thesecond frequency is about 19.9 Hz. This dual frequency capability isparticularly useful in tiltrotor aircraft applications, as the rotorsfor such aircraft generate one harmonic vibration while in airplanemode, and another harmonic vibration while in helicopter mode. A pumpingmeans 1079 (not shown in detail) is operably associated with tuner 1073for sliding tuner 1073 between the extended and retracted positions.

An actuator housing 1055 that houses a plurality of piezoceramicactuators 1057 is rigidly connected to a vibrating structure, such as awing spar 1061. In addition, actuator housing 1055 is resilientlycoupled to main housing 1053 by an elastomeric seal 1059. Eachpiezoceramic actuator 1057 is held in place at one end by a firstpreload screw 1081 carried by piston 1063, and held in place at theother end by a second preload screw 1083 carried by actuator housing1055. In this manner, piezoceramic actuators 1057 communicate withpiston 1063 only through actuator housing 1055. The primary stiffnessfor LIVE unit 1051 is provided by elastomer 1059.

An accumulator chamber 1085 for collecting air and other gas bubbles inthe system is disposed within main housing 1053. A tiny fluid passage1087 extends from the top of upper fluid chamber 1067 to the bottom ofaccumulator chamber 1085. In embodiments where accumulator chamber 1085is not located at the top of main housing 1053, it is preferred that apreloaded one-way valve 1089 be disposed within fluid passage 1087 to“pump” the bubbles down into accumulator chamber 1085. This pumpingaction is possible due to the sinusoidal oscillating pressure in upperfluid chamber 1067 relative to the steady pressure of accumulatorchamber 1085. During every cycle of higher pressure in upper fluidchamber 1067, one-way valve 1089 opens, thereby allowing the gas bubbleto flow through fluid passage 1087, and eventually, into accumulatorchamber 1085. Pre-loaded one-way valve 1089 allows steady pressurerelief, i.e., balance, without allowing oscillatory pressure intoaccumulator chamber 1085, which is to be avoided, as such oscillatorypressure in accumulator chamber 1085 affects the system dynamics, i.e.,may shift the tuning frequency.

Referring now to FIGS. 17A-21 in the drawings, additional alternateembodiments of the piezoelectric liquid inertia vibration eliminatoraccording to the present invention are illustrated. The presentinvention represents a means for producing active vibration attenuationfor reducing vibration in critical areas of rotorcraft airframes usingself-actuating structures, sensors, and control algorithms that resultin systems with minimum weight and power requirements. Theseself-actuating structures utilize piezoelectric actuation to enableactive vibration suppression combined with passive attenuation of rotorinduced vibration. Thus, the embodiments of FIGS. 17A-21 areparticularly well suited for crew seat mounts and payload mounts inrotorcraft and other aircraft. However, it should be understood that thepiezoelectric liquid inertia vibration eliminators shown in FIGS. 17A-21may be used in a wide variety of applications.

Referring now specifically to FIG. 17A in the drawings, a piezoelectricLIVE unit 1001 is illustrated in a cross-sectional view. LIVE unit 1001is a localized active vibration treatment that can be used to isolate apayload, such as a crew seat in a rotorcraft, from a vibratingstructure, i.e., a fuselage subject to main rotor b/rev vibration. Thevibrating structure (not shown) is coupled to a piston 1002 housed in apiston housing 1004.

LIVE unit 1001 includes a hydraulically amplified piezoactuator module1003 for housing two axially aligned piezoceramic stacks 1005 and 1007.Piezoceramic stacks 1005 and 1007 include piezoceramic actuators 1009and 1011 that are preferably on the line-of-action of the static loadpath. Piezoceramic actuators 1009 and 1011 selectively actuate astroke-amplifying piston 1013. Piston 1013 is held in place by anelastomeric seal 1015. Piston 1013, elastomeric seal 1015, andpiezoactuator module 1003 define two fluid chambers 1017 and 1019 withinpiezoactuator module 1003. A tuning unit 1021 is coupled topiezoactuator module 1003, such that a fluid tuning passage 1023 is influid communication with fluid chambers 1017 and 1019. A selected tuningfluid is disposed within fluid chambers 1017 and 1019 and fluid tuningpassage 1021. Piezoceramic stacks 1005 and 1007 operate out-of-phase toaugment the motion of the fluid tuning mass.

LIVE unit 1001 actively attenuates transmissibility between the fuselageand crew seat. It will be appreciated that the LIVE unit 1001 is readilytransportable to active mounts for other sensitive components on anymanned or unmanned rotorcraft.

Referring now specifically to FIG. 17B in the drawings, a chart 1022demonstrates an active attenuation for LIVE mount 1501 of greater than99% (−40 dB) over a wide frequency band, i.e., from 13.5 to 30 Hz, withvery low power requirements, for example, less than 4 W. It will beappreciated that the 30-Hz upper frequency limitation is from aswitching amplifier power supply system used during the test, not frompiezoceramic actuators 1009 or mount hardware.

Referring now specifically to FIG. 17C in the drawings, anotherpiezoelectric LIVE unit 1030 is illustrated in a cross-sectional view.LIVE unit 1030 is also a localized active vibration treatment that canbe used to isolate a payload, such as a crew seat in a rotorcraft, froma vibrating structure, i.e., an airframe 1032 subject to main rotorb/rev vibration. Airframe 1032 is coupled to a piston 1034 housed in apiston housing 1036. Piston 1034 is resiliently carried within housingby elastomeric seals 1035.

LIVE unit 1030 includes a hydraulically amplified piezoactuator module1038 for housing two axially aligned piezoceramic stacks 1040 and 1042.Piezoceramic stacks 1040 and 1042 include piezoceramic actuators 1044and 1046 that are preferably on the line-of-action of the static loadpath. Piezoceramic actuators 1044 and 1046 selectively actuate astroke-amplifying piston 1048. Piston 1048 is held in place byelastomeric seals 1050. Piston 1034, elastomeric seals 1035, piston1048, and elastomeric seals 1050 define two fluid chambers 1052 and 1054within LIVE unit 1030. A selected tuning fluid is disposed within fluidchambers 1052 and 1054. Piezoceramic actuators 1044 and 1046 operateout-of-phase to augment the motion of the fluid tuning mass.

LIVE unit 1030 actively attenuates transmissibility between airframe1032 and the crew seat of other isolated object. It will be appreciatedthat the LIVE unit 1030 is readily transportable to active mounts forother sensitive components on any manned or unmanned rotorcraft.

Referring now specifically to FIG. 18 in the drawings, anotherpiezoelectric LIVE unit 1101 is illustrated in a cross-sectional view.In this embodiment, a housing 1103 having a mounting portion 1105 housestwo axially aligned piezoceramic actuators 1107 and 1109. Housing 1103includes mounting brackets 1102 to facilitate the connection of LIVEunit 1101 to a vibrating structure (not shown).

Piezoceramic actuators 1107 and 1109 selectively actuate a stokeamplifying piston 1113. Piston 1113 is held in place by elastomericseals 1115. Housing 1103, piston 1113, and elastomeric seals 1115 definetwo fluid chambers 1117 and 1119 within housing 1103. A coiled fluidtuning passage 1123, preferably disposed within the walls of housing1103, is in fluid communication with fluid chambers 1117 and 1119. Aselected tuning fluid is disposed within fluid chambers 1117 and 1119and fluid tuning passage 1123. Piezoceramic actuators 1107 and 1109operate out-of-phase to augment the motion of the fluid tuning mass.

Referring now specifically to FIGS. 19A-19C in the drawings, theequations for the isolation frequency, the area ratios, and the lengthand number of turns of the fluid tuning passage for LIVE unit 1101 ofFIG. 18, respectively, are illustrated. It will be appreciated thatthese equations will vary depending upon the configuration of the LIVEunit.

Referring now specifically to FIGS. 20A and 20B in the drawings, anotherpiezoelectric LIVE unit 1201 is illustrated in longitudinal andtransverse cross-sectional views. In this embodiment, a housing 1203houses two axially aligned piezoceramic actuators 1207 and 1209. Housing1203 houses a piston 1202 to facilitate the connection of LIVE unit 1201to a vibrating structure (not shown).

Piezoceramic actuators 1207 and 1209 selectively actuate astroke-amplifying piston 1213. Piston 1213 is held in place byelastomeric seals 1215. Housing 1203, piston 1213, and elastomeric seals1215 define two fluid chambers 1217 and 1219 within housing 1203. Afluid tuning passage 1223 having a first set of coils 1225 and a secondset of coils 1227 is in fluid communication with fluid chambers 1217 and1219. A selected tuning fluid is disposed within fluid chambers 1217 and1219 and fluid tuning passage 1223. Piezoceramic actuators 1207 and 1209operate out-of-phase to augment the motion of the fluid tuning mass.

Referring now to FIG. 21 in the drawings, a mechanical equivalent model1251 representative of the LIVE units of FIGS. 17A, 17C, 18, 20A, and20B is illustrated. Mechanical equivalent model 1251 includes avibrating mass 1253 and an isolated mass 1255 coupled together through atunable LIVE unit comprising a spring 1057, a first tuning mass 1059, asolid-state actuator 1061, and an optional second tuning mass 1063 shownin dashed lines. Solid-state actuator 1061 enhances the operation oftuning masses 1059 and 1063. Solid-state actuator 1061 is preferably apiezoceramic actuator, but may be an electrostrictive material, amagnetostrictive material, or any other suitable solid-state actuator.

It will be appreciated that the LIVE unit 1001 of FIG. 17 would includesecond tuning mass 1063, but that LIVE units 1101 and 1201 of FIGS. 18and 20A and 20B would not include second tuning mass 1063, although LIVEunits 1101 and 1201 do include a very small amount of mass that may beconsidered as second tuning mass 1063. It will be further appreciatedthat solid-state actuator 1061 is 180.degree. out of phase as comparedwith active tuning element 415 of FIG. 6A.

Referring now to FIGS. 22A and 22B in the drawings, another embodimentof the tunable vibration isolator of the present invention isillustrated. In this embodiment, a vibration absorbing Frahm, or tunedmass absorber, is modified with active piezoceramic tuning elements.FIG. 22A shows a simplified schematic of an exemplary piezoelectricfrahm 1301 in a cross-sectional view; and FIG. 22B shows a mechanicalequivalent model 1303 for piezoelectric frahm 1301.

Piezoelectric Frahm 1301 includes a Frahm housing 1305 that houses aFrahm absorber mass 1307. Frahm absorber mass 1307 is suspended withinFrahm housing 1305 by a spring member 1309. A mounting structure 1311 isrigidly coupled to a vibrating mass 1313, such as an aircraft fuselage.Frahm housing 1305 is coupled to mounting structure 1311 via a solidstate actuator, preferably at least one piezoceramic actuator 1315.

With this configuration, piezoceramic actuators 1315 are in series withspring member 1309, thereby allowing the piezoceramic actuators 1315 tochange the mobility of Frahm housing 1305. This results in a lighterFrahm, i.e., moving mass, being able to achieve the same level ofvibration reduction as a much heavier Frahm. This is done by increasingthe amplification factor, Q=1/(2ξ), by decreasing the Frahm damping, ξ.

In addition, slight variations in the Frahm operating frequency can beachieved through active re-tuning with piezoceramic actuators 1315;however, it should be understood that such re-tuning may require apiezoactuator gain mechanism, depending upon the degree of frequencyshift.

This embodiment of the present invention solves the problem of dampingthat reduces the effectiveness of the moving mass. In addition, thisembodiment provides a means for making the Frahm less sensitive wheninstalled on structures with different impedances.

Referring now to FIGS. 23A and 23B in the drawings, another embodimentof the present invention is illustrated. In this embodiment, two novelfeatures have been combined into a single, modular LIVE unit 1401. LIVEunit 1401 includes a dual frequency LIVE portion 1403 and a multistagepiezo-pumper portion 1405. FIG. 23A shows a simplified schematic of LIVEunit 1401 in a cross-sectional view; and FIG. 23B shows a mechanicalequivalent model 1402 of LIVE unit 1401.

LIVE portion 1403 includes a housing 1407 having a mounting portion 1409adapted for connection to a body for which it is desirable to isolatevibration, i.e., an isolated body. A piston 1411 is resiliently coupledto housing 1407 by elastomeric seals 1413. Housing 1407, piston 1411,and elastomeric seals 1413 define an upper fluid chamber 1415 and alower fluid chamber 1417.

A primary tuning port 1419 is in fluid communication with both upperfluid chamber 1415 and lower fluid chamber 1417. Primary tuning port1419 is configured to allow Isolation of harmonic vibration at a firstselected frequency. A secondary tuning port 1421 is also in fluidcommunication with both upper fluid chamber 1415 and lower fluid chamber1417. In the preferred embodiment, a spring-mass system 1423 is operablyassociated with secondary tuning port 1421. Spring-mass system 1423creates a new degree of freedom. Secondary tuning port 1421 allowsisolation of harmonic vibration at a second selected frequency. It willbe appreciated that the mass of spring-mass system 1423 may be zero,allowing the fluid in secondary tuning port 1421 to function as the massoperating against the spring in spring-mass system 1423. It will befurther appreciated that additional tuning ports may be added forapplications in which it is desirable to isolate additional harmonicfrequencies.

A multistage piezo-pumper portion 1405 includes a housing 1431 thathouses a piston 1433. Piston 1433 is resiliently coupled to housing 1431by elastomeric seals 1435. Housing 1431, piston 1433, and elastomericseals 1435 define a first fluid chamber 1437 and a second fluid chamber1439. First fluid chamber 1437 is in fluid communication with upperfluid chamber 1415, and second fluid chamber 1439 is in fluidcommunication with lower fluid chamber 1417. Piston 1433 is actuated byat least one piezoceramic actuator 1441.

In this manner, piezoceramic actuators 1441 actively augment thevibration attenuation capability of LIVE unit 1401 in both the firstselected frequency range and the second selected frequency range. LIVEunit 1401 is capable of providing greater than 99% isolation in widefrequency ranges with extremely low power. Low power can be achievedbecause piezoceramic actuator 1441 operates at close to a 90 degreephase angle. It should be understood that the dual frequencypiezoactuator feature and the multistage piezo-pumper may be utilizedindependently of each other in a vibration isolation system.

Mechanical equivalent model 1402 includes a vibrating mass 1404 and aisolated mass 1406 separated by a tunable LIVE unit 1408. It will beappreciated that the positions of vibrating mass 1404 and isolated mass1406 may be reversed without affecting the operation of the system. Inthe example of FIG. 23B, vibrating mass 1404 is an airframe and isolatedmass 1406 is a sight system.

Tunable LIVE unit 1408 comprises at least one spring 1440, at least onesolid-state actuator 1410, a first tuning mass 1412, a second tuningmass 1414, and a second spring 1416. In this case, spring 1440represents elastomeric seals 1413; first tuning mass 1412 representsprimary tuning port 1419, second tuning mass 1414 and second spring 1416represent spring-mass system 1423; and solid-state actuator 1410represents piezoceramic actuators 1435 and 1441. It should be understoodthat mechanical equivalent model 1402 is representative of a widevariety of configurations and applications of tunable LIVE units.

Referring now to FIGS. 24-27 in the drawings, another embodiment of thetunable vibration isolation system according to the present invention isillustrated. This embodiment relates to an active vibration LIVE mountsystem 1501 that is particularly well suited for rotating machineryincluding diesel engines, gas turbine engines, generator sets, andgearboxes. The LIVE mount 1501 is lightweight, low cost, and has verylow power requirements, i.e., virtually no heat loss. This embodimentwill be described with reference to rotating machinery on a naval vesselor ship.

To maximize survivability and mission effectiveness, acoustic radiationfrom a ship must be carefully controlled. This requires treatment ofboth external noise sources such as the rotating propeller and hullslamming, and internal noise sources. Of primary concern for internalnoise is precluding structural-borne vibration transmission fromrotating machinery to the ship's hull structure, particularly in thefrequency range of hull natural frequencies.

In the preferred embodiment, the ship's primary propulsion is providedby diesel engines and the electrical power is provided by dieselengine-generator sets, both of which have 12-piston, 4-stroke dieselswith the same approximate maximum speed of 1,800 rpm. Therefore thevibration treatment system described can be directly applied to saiddiesel engine and said diesel-generator sets.

Referring now to FIG. 24 in the drawings, the vibration generated bysaid diesel engine will be described. The vibration generated by saiddiesel engine consists principally of 1/rev, 3/rev, and 12/rev, that is,1 cycle of vibration per revolution, 3 cycles of vibration perrevolution, and 12 cycles of vibration per revolution. As shown ingraphs 1531, 1533, and 1535, the torque pulses are spaced 30°, 90°, 30°,90°, etc. A simple Fourier series can be used to illustrate the harmoniccomponents of cos 3ωt and cos 12ωt. In addition, the 1/rev term (notshown in FIG. 28) will be present due to any mass imbalance.

Point-of-source vibration attenuation is the most effective means ofstructure-borne vibration treatment, especially when localized “choke”points exist within the design. The traditional approach has been to usesoft elastomeric mounts that place the engine's mounted naturalfrequency low, i.e., less than 70% of the excitation frequency. Thisprovides attenuation in the range of 40%, i.e., transmissibility of 60%,or −8 dB. The stiffness must be appropriate to support the engine weightand torque.

The mounted roll, i.e., about the torque-axis, natural frequency of thediesel engine in the preferred embodiment with the prior art is 3.9 Hz,which provides a natural attenuation of 82% (−15 dB) of 1/rev at engineidle (600 rpm). Neglecting the structural compliance of ship, themounted vertical natural frequency of the diesel engine with prior artis 7.1 Hz, which provides a natural attenuation of only 4% (−0.4 dB).

According to the present invention, LIVE mount 1501 is used in place ofthe soft mounts and augmented to cancel harmonic vibrations withextremely low power requirements through the use of embeddedpiezoceramic actuators 1541 (see FIG. 25A). In addition to exceptionalpassive treatment, by utilizing piezoceramic actuators 1541, LIVE mount1501 provides active means of canceling vibration, resulting inbroadband attenuation of 99.6% isolation (−48 dB). Piezoceramicactuators 1541 attenuate transmissibility between the vibrating body andisolated body.

Referring now to FIGS. 25A and 25B in the drawings, the operation ofLIVE mount 1501 will be described. FIG. 25A shows a simplified schematicof LIVE mount 1501 in a cross-sectional view; and FIG. 25B shows amechanical equivalent model 1551 for LIVE mount 1501. LIVE mount 1501includes a housing 1553. A piston 1555 is resiliently coupled to housing1553 by elastomeric seals 1557. Piston 1555 includes an axial tuningport 1556. The diesel engine is rigidly coupled to piston 1555, andhousing 1553 is rigidly coupled to said ship.

At least one piezoceramic actuator 1541 is operably associated withhousing 1553. In FIG. 30A, piezoceramic actuators 1541 are coupled torigid diaphragms 1559. Diaphragms 1559 are resiliently sealed to housing1553 by seals 1561. Housing 1553, piston 1555, elastomeric seals 1557,diaphragms 1559, and seals 1561 define an upper fluid chamber 1563 and alower fluid chamber 1565. Upper fluid chamber 1563 and lower fluidchamber 1565 are in fluid communication through tuning port 1556. Upperfluid chamber 1563, lower fluid chamber 1565, and tuning port 1556 arecompletely filled with an inviscid, dense fluid and pressurized toprevent cavitation. The product of the fluid volume and the fluiddensity defines the tuning mass, m_(t).

As is shown on mechanical equivalent model 1551, the area ratio, R_(l),of housing 1553 to tuning port 1556 is analogous to the length ratio ofthe arms, b/a; the elastomeric spring 1557 is analogous to themechanical spring, k_(e); and the inertial effect of tuning port 1556 isanalogous to the inertial effect of the tuning mass m_(t) on themechanical arm.

As piston 1555 moves up or down, it forces fluid to move in the oppositedirection, producing an inertial force that cancels the elastomericspring force at a discrete frequency, known as the passive isolationfrequency or antiresonance, defined below.

$\begin{matrix}{f_{iso} = {\frac{1}{2\; \pi}\sqrt{\frac{k_{e}k_{p}}{{k_{e}\left( {m_{p} + {R_{1}^{2}m_{t}}} \right)} + {k_{p}m_{t}{R_{1}\left( {R_{1} - 1} \right)}}}}}} & {{Equation}\mspace{11mu} (1)}\end{matrix}$

The piezoceramic actuator stiffness and mass is represented by k_(p) andm_(p), respectively. For simplicity, Equation (1) assumes the combinedstiffness, k_(ee), of the fluid, i.e., bulk modulus, and the containmentvessel is infinite, and Rp=1, i.e., d=c.

Several features of the LIVE mount 1501 make it an efficient applicationof piezoceramic actuators. First, the piezoceramic material is not inthe primary steady-load path, and thus, does not need to be sized forcritical static load conditions. Second, the fluid is utilized both asinertia to create an antiresonance, as well as, for hydraulicallyamplifying the actuator stroke. Finally, because piezoceramic actuators1541 are only required to augment the passive performance, their sizeand attendant cost remain small, even for large applications like marinepropulsion systems.

Piezoceramic actuators 1541 are preferably commanded using a Multi-PointAdaptive Vibration Suppression System (MAVSS) algorithm to augment theantiresonance characteristics of LIVE mount 1501, resulting in dramaticreduction in vibration transmissibility into the structure of ship 1503.The MAVSS control algorithm, is an inherently stable, yet robust timedomain control methodology that uses traditional Higher Harmonic Control(HHC) techniques of identifying the Fourier components of thedisturbance at the frequencies of interest, and generating the controlcommand necessary to cancel these disturbances by inverting the plantdynamics at each particular frequency. The MAVSS is programmed to cancelmultiple harmonics, for example, both the 1/rev vibration and 3/revvibration simultaneously. In addition to the system identificationaspects of the MAVSS algorithm, an additional feature is the use of anobjective function that includes both disturbance and control effort togovern the feedback control process.

The MAVSS control gain matrix is calculated based on the identifiedresponse from the control actuators to the performance sensors, T. Inpractice, the sine and cosine components of this response are identifiedusing a finite-difference approach. With this transfer function matrixidentified, the MAVSS control gain is calculated as:

K=[T′R _(s) T+Q] ⁻¹ T′R _(s)  (1)

where Q is a matrix penalizing the input to each actuator, i.e., controlpenalty, and R_(s) is a matrix penalizing the response of each sensor,i.e., performance weighting. The control penalty is reduced to a scalarvalue by setting Q=ρl, where l is the identity matrix. This produces anequal control penalty for each actuator. Likewise, setting R_(s)=lproduces an equal performance weight for each sensor. The MAVSS controlinput can be calculated as:

u _(new) =α·K·Z+u _(old)  (2)

where u_(new) is the control input for the next integer number of rotorrevolutions, Z is the response at the performance sensors, and u_(old)is the previous control input. As the control penalty is relaxed (cheapcontrol asymptote), K becomes T⁻¹, and the control input produces aresponse at the sensors equal and opposite to the hub disturbances,resulting in zero response by superposition.

For this system, each LIVE mount 1501 preferably has one verticalaccelerometer mounted on the vibrating body-side of LIVE mount 1501. TheMAVSS system remains stable and continues to operate in the event of afailure of one or more sensors. In the preferred embodiment for use onmarine propulsion systems, the MAVSS senses engine rpm and automaticallytracks the harmonic vibration as the engine's speed changes.

Referring now to FIGS. 26A-26C in the drawings, an exemplary mechanicaldesign for the LIVE mount of FIG. 25A is illustrated. A LIVE mount 1601includes a housing 1603 for housing a piston 1605. Piston 1605 isresiliently carried within housing 1603 by elastomeric seals 1607. Amount plate 1609 configured for attachment to a diesel engine isconnected to piston 1605. In the preferred embodiment, four mechanicalsprings 1601 disposed between mount plate 1609 and housing 1603 are usedto prevent the static creep inherent in elastomerics. Housing 1603,piston 1605, and elastomeric seals 1607 define an upper fluid chamber1611 and a lower fluid chamber 1613. It is preferred that housing 1603be made from aluminum.

Elastomeric seals 1607 preferably provide vertical stiffness of 23,000lb/in and transverse stiffness of 30,000 lb/in. An optional skirt (notshown) may be added around mount plate 1609 to protect the elastomericelements from oil contamination. An up and down overtravel stop 1615 isoperably associated with piston 1605 to prevent excessive loading to theelastomerics. It is preferred that overtravel stop 1615 be positionedsuch that contact does not occur under normal operation. In thepreferred embodiment, an accelerometer 1617 is located on the base ofhousing 1603 as the feedback sensor in the above.

Housing 1603 also houses a piezo-piston 1619. Piezo-piston 1619 isresiliently carried within housing 1603 by elastomeric seals 1621.Housing 1603, piezo-piston 1619, and elastomeric seals 1621 furtherdefine upper fluid chamber 1611 and lower fluid chamber 1613. Upperfluid chamber 1611 and lower fluid chamber 1613 are in fluidcommunication via an elongated tuning port 1620 that preferably coilsaround housing 1603.

Piezo-piston 1619 is driven by a stack of at least two piezoceramicactuators 1623. Piezoceramic actuators 1623 are preferably stacked in apush-pull fashion for reliability. If one piezoceramic actuator 1623fails, the stack will continue to operate with the remaining healthypiezoceramic actuator 1623. This push-pull arrangement provides anenergy efficient design, as is discussed in more detail below.Piezoceramic actuators 1623 are positioned on opposing sides ofpiezo-piston 1619 having a piezo area ratio, R_(p).

LIVE mount 1601 provides an effective piston diameter with a tuning portinner diameter. This provides a LIVE area ratio, R_(I). The tuning port1620 is coiled around housing 1603 to provide the appropriate fluidtuning mass, m_(t), to provide optimum passive isolation frequency perEquation (1). Though not shown, it is preferred that tuning port 1620 beencased within a protective structure, such as a casting. Anair-to-fluid accumulator 1625 with sight glass allows thermal expansionof the fluid while maintaining the appropriate pressure to precludecavitation during operation.

Referring now to FIG. 27 in the drawings, a chart 1645 depicting thevibration attenuation of LIVE mount 1601 is illustrated. LIVE mount 1601is expected to reduce the structure-borne mechanical noise signaturebelow 100 Hz by more than 99% relative to rigid body response (40 dB).Analytical simulations actually show 99.9% reduction (−60 dB). As isshown, LIVE mount 1601 is capable of 99.9% vibration attenuation (−60dB) at both 1/rev and 3/rev. However, in practical application thislevel of reduction is probably below the ambient noise level.

Using a switching amplifier power supply, energy is swapped between theamplifier and capacitive load with low losses. This approach can resultin an energy savings on the order of 75%. Additionally, because LIVEmount 1601 utilizes piezoceramic actuator pairs being simultaneouslydriven out of phase, i.e., push-pull, energy recovery during each cycleis provided.

It is apparent that an invention with significant advantages has beendescribed and illustrated. Although the present invention is shown in alimited number of forms, it is not limited to just these forms, but isamenable to various changes and modifications without departing from thespirit thereof.

The particular embodiments disclosed above are illustrative only, as theapplication may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. It is therefore evident that the particularembodiments disclosed above may be altered or modified, and all suchvariations are considered within the scope and spirit of theapplication. Accordingly, the protection sought herein is as set forthin the description. It is apparent that an application with significantadvantages has been described and illustrated. Although the presentapplication is shown in a limited number of forms, it is not limited tojust these forms, but is amenable to various changes and modificationswithout departing from the spirit thereof.

What is claimed is:
 1. A vibration isolator comprising: a housing; apiston resiliently disposed within the housing; a first fluid chamberand a second fluid chamber defined by the housing and the piston; atuning passage placing the first fluid chamber and the second fluidchamber in fluid communication; a tuning mass disposed within the tuningpassage; a tuner configured to telescope within the tuning passage andextend into the second fluid chamber to adjust the frequency of thetuning mass; and at least one actuator rigidly coupled to a vibratingstructure and resiliently coupled to the housing for selectivelytransferring forces to the housing.
 2. The vibration isolator accordingto claim 1, wherein the tuning mass is a fluid.
 3. The vibrationisolator according to claim 1, further comprising: at least one flowdiverter aligned with the tuning passage for directing the flow of atuning fluid.
 4. The vibration isolator according to claim 1, whereinthe actuator is a piezoceramic actuator.
 5. The vibration isolatoraccording to claim 1, wherein the actuator is an electromagneticactuator.
 6. The vibration isolator according to claim 1, wherein theactuator is a pneumatic actuator.
 7. The vibration isolator according toclaim 1, wherein the actuator is a hydraulic actuator.
 8. The vibrationisolator according to claim 1, wherein the actuator is a piezoelectricactuator.
 9. The vibration isolator according to claim 1, wherein theaxial length of the tuning passage is selectively adjusted.
 10. Thevibration isolator according to claim 1, further comprising: a pump incommunication with the tuner and configured to translate the tunerbetween an extended and a retracted position.
 11. The vibration isolatoraccording to claim 1, further comprising: a gas accumulation chamber influid communication with the first fluid chamber for collecting andaccumulating gas from the first fluid chamber, the second fluid chamber,and the tuning passage.
 12. The vibration isolator according to claim11, wherein the gas accumulation chamber permits steady state pressurerelief within the housing while avoiding oscillatory pressure.